Compared with a conventional macro base station, the system of a distributed base station is divided into a base band unit (BBU) and a remote radio frequency unit (RRU). The RRU is deployed at an access point far from the BBU. The RRU and the BBU are connected through an optical fiber, and baseband radio signals are transmitted there between in analog or digital mode. The distance between the BBU and the RRU generally ranges from dozens of meters to one or two hundred meters. In this way, network construction is more flexible and convenient, and antenna deployment is not affected by the location of an equipment room. In addition, a base station system can be designed with a large capacity and the cost of system construction may be reduced. A distributed antenna system (DAS) is similar to a distributed base station having an RRU. However, the distance between the BBU and the RRU may be extended to several hundreds of meters, or even to tens of hundreds of meters. In addition to using a direct optical fiber for connection, optical transmission technologies, such as the passive optical network (PON) and wave division multiplexing (WDM) may also be used for connection. Further, preferably a multi-cell joint processing manner, such as network multiple input and multiple output (MIMO), multi-cell joint scheduling, is used to reduce interference between cells and further increase a system capacity.
As 3rd generation (3G)/4th generation (4G) technologies, such as Long Term Evolution (LTE), emerge, the radio spectral width increases (20 MHz to 100 MHz). Meanwhile, an RRU generally supports multi-antenna technologies, such as MIMO. As such, the bandwidth required for transmitting baseband radio signals between the BBU and the RRU increases. For example, when LTE baseband in-phase/quadrature (I/Q) signals of 20 MHz bandwidth are transmitted by using a digital manner, the rate for transmitting baseband radio signals by each RRU is as high as 10 Gbit/s. Apparently, this imposes great challenges to transmission of baseband signals between the BBU and the RRU. Typically, a single BBU may be connected to dozens to hundreds of RRUs. This means that the baseband radio signal routing and switching unit of each BBU needs to route and switch dozens to hundreds of paths of radio signals whose transmission rates each is as high as 10 Gbit/s. This does not include data exchange between radio access processing modules. Apparently, this imposes great challenges to implementation of the BBU. When the cloud computing architecture cloud radio access network (C-RAN) is further used, a large number of high-speed baseband radio signals need to be transmitted and exchanged between BBUs, which imposes great challenges to design and reliable running of an entire C-RAN system. Therefore, it becomes crucial to effectively compress baseband radio signals, to lower the bandwidth requirement for transmitting baseband signals between the BBU and the RRU and reduce the complexity of the BBU and a C-RAN system in which multiple BBUs are interconnected. In the prior art, four manners are generally available to implementation of compression of baseband radio signals, that is, sampling rate reduction, non-linear quantization, intelligence quotient (IQ) data compression, and subcarrier compression.
All the four technologies for compressing baseband radio signals, however, face a common problem: Because the transmission rate of a baseband signal is extremely high, the four manners are highly complicated, and the performance may be greatly degraded.